Several techniques presently exist for measuring liquid/liquid interfacial tension for the purpose of predicting surfactant performance. Among them are the spinning drop method, the shear field method, the electric field method, the duNouy ring method, the sessile/pendant drop method, and the drop weight method.
Of the methods referred to above the drop weight method is the most similar to the methods disclosed herein, but the methods according to the invention are considerably simpler and more effective for their purpose than is the drop weight method.
In the drop weight method of measuring interfacial tension the weight of each drop is measured in a laborious manner: after each liquid drop has formed and detached, the reservoir of liquid being dispersed by the surfactant is manually weighed. The difference in weight before and after the drop detachment is assumed to be the drop weight. This approach is labor intensive and subject to high probability of producing erroneous data due to human intervention and manipulation.
The drop weight method relies upon Tate's Law extended by the Scheele and Meister development work and modified by Harkin's correction factor due to the necessity of accounting for the fluid volume remaining attached to the dispensing fluid orifice after detachment of each liquid drop. Tate's Law, as modified by Sheele and Meister, is applicable only in those cases in which no surfactant is present in the liquid into which the drop is dispensed and the Harkin's correction is applied to account for liquid left at the dispensing orifice following detachment of a drop.
None of the known methods referred to above for measuring liquid/liquid interfacial tension provides any information with respect to the dynamic aspects of interfacial tension reduction of a liquid/liquid interface by a surfactant. In the methods disclosed herein, however, a measure of the dynamic aspects of such interfacial tension reduction is obtainable.
Among the objects of the present invention is to simplify the measurement of liquid/liquid interfacial tension primarily for the purpose of evaluating the effectiveness of surfactants on various immiscible liquids.
Another object of the invention is to provide a method for the evaluation of the dynamic characteristics of interfacial tension reduction due to the presence of surfactants.